Field of the Invention
The present invention relates to a technology of controlling an image forming condition.
Description of the Related Art
An electrophotographic image forming apparatus is configured to charge toner particles to form an image using an electrostatic force. Therefore, when a charge amount of the toner particles changes, density and quality of an output image may change in accordance with the change. The charge amount of the toner particles significantly changes depending on usage environment, the density of the output image, elapsed time from the output, and other factors. Therefore, the output image may fluctuate depending on various conditions when control to stabilize the output is not performed.
The image forming apparatus is configured to form an image using a developer containing toner particles and carrier particles. This image forming apparatus is configured to limit toner supply based on a result of detecting the amount of toner particles. In this image forming apparatus, the charge amount of the toner particles changes depending on a mixing ratio (T/C ratio) of toner particles to carrier particles in a developing device. That is, when the ratio of the toner particles decreases, the charge amount of the toner particles increases. When the charge amount of the toner particles increases, the amount of toner particles that adhere to a latent image having a certain charge decreases to cause a decrease in image density. In contrast, when the ratio of the toner particles increases, the charge amount of the toner particles decreases. When the charge amount of the toner particles decreases, the amount of toner particles that adhere to a latent image having a certain charge increases to cause increase in image density.
To address this problem, the image forming apparatus is configured to form a measurement image to perform feed-back control of controlling the toner supply amount based on the amount of toner adhering to the measurement image, which is measured by a sensor. However, toner supply control causes downtime because image forming conditions are corrected after the amount of toner adhering to the measurement image is measured. Further, there has been a problem in that it takes time to change the charge amount of the toner particles in the developing device after the toner supply.
In view of this, as a technology for solving those problems, there is known a technology of estimating the charge amount of the toner particles, to thereby control the image forming conditions in real time (U.S. Pat. No. 8,335,441).
In the image forming apparatus described in U.S. Pat. No. 8,335,441, a stirring time constant of the toner charge amount and a charge eliminating time constant of the toner charge amount are regarded as constant values.
However, the time constants change depending on the environment in which the image forming apparatus is placed and other factors. When the time constants change, a predicted value of the toner charge amount may be deviated from the actual toner charge amount, and thus the density of the image formed based on the image forming conditions suitable for the predicted value of the toner charge amount may differ from a target density.